Wendi Heinzelman - Academia.edu (original) (raw)

Papers by Wendi Heinzelman

Coverage preservation is one of the basic QoS requirements of wireless sensor networks, yet this ... more Coverage preservation is one of the basic QoS requirements of wireless sensor networks, yet this problem has not been sufficiently explored in the context of cluster-based sensor networks. Specifically, it is not known how to select the best candidates for the cluster head roles in applications that require complete coverage of the monitored area over long periods of time. In this paper, we take a unique look at the cluster head election problem, specifically concentrating on applications where the maintenance of full network coverage is the main requirement. Our approach for cluster-based network organization is based on a set of coverage-aware cost metrics that favor nodes deployed in densely populated net- work areas as better candidates for cluster head nodes, active sensor nodes and routers. Compared with using traditional energy-based selection methods, using coverage-aware selection of cluster head nodes, active sensor nodes and routers in a clustered sensor net- work increases the time during which full coverage of the monitored area can be main- tained anywhere from 25% to 4.5 , depending on the application scenario.

Visual sensor networks have emerged as an important class of sensor-based distributed intelligent... more Visual sensor networks have emerged as an important class of sensor-based distributed intelligent systems, with unique performance, complexity, and quality of service challenges. Consisting of a large number of low-power camera nodes, visual sensor networks support a great number of novel vision-based applications. The camera nodes provide information from a monitored site, performing distributed and collaborative processing of their collected data. Using multiple cameras in the network provides different views of the scene, which enhances the reliability of the captured events. However, the large amount of image data produced by the cameras combined with the network’s resource constraints require exploring new means for data processing, communication, and sensor management. Meeting these challenges of visual sensor networks requires interdisciplinary approaches, utilizing vision processing, communications and networking, and embedded processing. In this paper, we provide an overview of the current state-of-the-art in the field of visual sensor networks, by exploring several relevant research directions. Our goal is to provide a better understanding of current research problems in the different research fields of visual sensor networks, and to show how these different research fields should interact to solve the many challenges of visual sensor networks.

Organizing wireless sensor networks into clusters enables the efficient utilization of the limite... more Organizing wireless sensor networks into clusters enables the efficient utilization of the limited energy resources of the deployed sensor nodes. However, the problem of unbalanced energy consumption exists, and it is tightly bound to the role and to the location of a particular node in the network. If the network is organized into heterogeneous clusters, where some more powerful nodes take on the cluster head role to control network operation, it is important to ensure that energy dissipation of these cluster head nodes is balanced. Oftentimes the network is organized into clusters of equal size, but such equal clustering results in an unequal load on the cluster head nodes. Instead, we propose an Unequal Clustering Size (UCS) model for network organization, which can lead to more uniform energy dissipation among the cluster head nodes, thus increasing network lifetime. Also, we expand this approach to homogeneous sensor networks and show that UCS can lead to more uniform energy dissipation in a homogeneous network as well.

Ad Hoc Networks, 2008

In mobile ad hoc networks, node mobility causes frequent link failures, thus invalidating the rou... more In mobile ad hoc networks, node mobility causes frequent link failures, thus invalidating the routes containing those links. Once a link is detected broken, an alternate route has to be discovered, incurring extra route discovery overhead and packet latency. The traffic is also interrupted at the transport layer, and proper traffic recovery schemes have to be applied. To reduce the frequency of costly route re-discovery procedures and to maintain continuous traffic flow for reliable transport layer protocols, we suggest discovering long lifetime routes (LLR). In this paper, we first propose g-LLR, a global LLR discovery algorithm, that discovers LLRs of different route lengths for any given pair of nodes. We then propose a distributed LLR discovery scheme (d-LLR) that discovers two of the most desirable LLRs through one best-effort route discovery procedure. Simulations show that the lifetimes of the routes discovered by d-LLR are very close to those discovered by g-LLR. Simulations also show that the performance of different transport layer protocols is greatly improved by using LLRs. More importantly, traffic can remain continuous using the provided LLRs. D-LLR can be implemented as an extension to existing ad hoc routing protocols, and it improves the performance of transport layer protocols without modifications on them.

In mobile ad hoc networks, node mobility causes links between nodes to break frequently, thus ter... more In mobile ad hoc networks, node mobility causes links between nodes to break frequently, thus terminating the lifetime of the routes containing those links. An alternative route has to be discovered once a link is detected as broken, incurring extra route discovery overhead and packet latency. A simple solution to reduce the frequency of this costly discovery procedure is to

IEEE Transactions on Mobile Computing, 2008

In multihop wireless sensor networks that are often characterized by many-to-one (convergecast) t... more In multihop wireless sensor networks that are often characterized by many-to-one (convergecast) traffic patterns, problems related to energy imbalance among sensors often appear. Sensors closer to a data sink are usually required to forward a large amount of traffic for sensors farther from the data sink. Therefore, these sensors tend to die early, leaving areas of the network completely unmonitored and reducing the functional network lifetime. In our study, we explore possible sensor network deployment strategies that maximize sensor network lifetime by mitigating the problem of the hot spot around the data sink. Strategies such as variable-range transmission power control with optimal traffic distribution, mobile-data-sink deployment, multiple-data-sink deployment, nonuniform initial energy assignment, and intelligent sensor/relay deployment are investigated. We suggest a general model to analyze and evaluate these strategies. In this model, we not only discover how to maximize the network lifetime given certain network constraints but also consider the factor of extra costs involved in more complex deployment strategies. This paper presents a comprehensive analysis on the maximum achievable sensor network lifetime for different deployment strategies, and it also provides practical cost-efficient sensor network deployment guidelines.

In multi-hop wireless sensor networks that are characterized by many-to-one traffic patterns, pro... more In multi-hop wireless sensor networks that are characterized by many-to-one traffic patterns, problems related to energy imbalance among sensors often appear. When each node has a fixed transmission range, the amount of traffic that the sensor nodes are required to forward increases dramatically as the distance to the data sink becomes smaller. Thus, sensors closest to the data sink tend to die early, leaving areas of the network completely unmonitored and causing network partitions. Alternatively, if all sensors transmit directly to the data sink, the furthest nodes from the data sink dies much more quickly than those close to the sink. While it may seem that network lifetime could be improved by use of a more intelligent transmission power control policy that balances the energy used in each node by requiring nodes further from the data sink to transmit over longer distances (although not directly to the data sink), such a policy can only have a limited effect. In fact, this energy balancing can be achieved only at the expense of gross energy inefficiencies. In this paper, we investigate the transmission range distribution optimization problem and show where these inefficiencies exist when trying to maximize the lifetime of many-to-one wireless sensor networks.

In this paper, we address a fundamental problem concerning the best flooding strategy to minimize... more In this paper, we address a fundamental problem concerning the best flooding strategy to minimize cost and latency for target discovery in wireless networks. Should we flood the network only once to search for the target, or should we apply a so-called "expansion ring" mechanism to reduce the cost? If the "expansion ring" mechanism is better in terms of the average cost, how many rings should there be and what should be the radius of each ring? We separate wireless networks based on network scale and explore these questions. We prove that two-ring and three-ring schemes can reduce the cost of flooding compared to a single attempt, and we provide a general formula to determine good parameters for the two-ring and three-ring hop-based flooding schemes. Through simulations, we show that choosing flooding parameters according to our techniques gives performance close to that of ideal flooding schemes. Afterwards, we extend our work from the single target discovery problem to the multi-target discovery problem. We show that a properly chosen searching radius can save much more searching cost than a simple radius selection scheme for multi-target discovery problems.

Sensor networks are becoming increasingly important as tools for monitoring remote environments. ... more Sensor networks are becoming increasingly important as tools for monitoring remote environments. As sensors are typically batteryoperated, it is important to efficiently use the limited energy of the nodes to extend the lifetime of the sensor network. Two factors can greatly influence the performance of protocols for these networksthe data delivery model, which describes how the end user wants to access the data, and the network dynamics, which include sensor mobility as well as changes in sensor data rates throughout the lifetime of the network. In this paper, we look at several media access control protocols for sending data from sensors to a local data collector. Comparing these protocols shows that there is an inherent tradeoff in energy efficiency with adaptability of the protocol.

In multi-hop wireless sensor networks that are characterized by many-to-one (converge-east) traff... more In multi-hop wireless sensor networks that are characterized by many-to-one (converge-east) traffic patterns, problems related to energy imbalance among sensors often appear. When the transmission range is fixed for nodes throughout the network, the amount of traffic that sensors are required to forward increases dramatically as the distance to the data sink becomes smaller. Thus, sensors closest to the data sink tend to die early. Network lifetime can be improved to a limited extent by the use of a more intelligent transmission power control policy that balances the energy used in each node by requiring nodes further from the data sink to transmit over longer distances (although not directly to the data sink). Alternatively, policies such as data aggregation allow the network to operate in a more energy efficient manner. Since the deployment of an aggregator node may be significantly more expensive than the deployment of an ordinary microsensor node, there is a cost tradeoff involved in this approach. This paper provides an analysis of these policies for mitigating the sensor network hot spot problem, considering energy efficiency as well as cost efficiency.

—Batteries of field nodes in a wireless sensor network pose an upper limit on the network lifetim... more —Batteries of field nodes in a wireless sensor
network pose an upper limit on the network lifetime. Energy
harvesting and harvesting aware medium access control
protocols have the potential to provide uninterrupted network
operation, as they aim to replenish the lost energy so that energy
neutral operation of the energy harvesting nodes can be achieved.
To further improve the energy harvesting process, there is a need
for novel schemes so that maximum energy is harvested in a
minimum possible time. Multi-hop radio frequency (RF) energy
transfer is one such solution that addresses these needs. With the
optimal placement of energy relay nodes, multi-hop RF energy
transfer can save energy of the source as well as time for the
harvesting process. In this work we experimentally demonstrate
multi-hop RF energy transfer, wherein two-hop energy transfer
is shown to achieve significant energy and time savings with
respect to the single-hop case. It is also shown that the gain
obtained can be translated to energy transfer range extension.

Intelligent systems like automatic highway traffic management, area surveillance, and geological ... more Intelligent systems like automatic highway traffic management, area surveillance, and geological activity monitoring require substantial data collection and processing in the field. Energy self-sustainability is a critical foundation for successful field systems that are away from the power grid infrastructure. Instead of the conventional battery-based energy storage, this paper argues that the super capacitor buffering of solar energy (SOLARCAP) has the advantages of precise energy lifetime awareness, low maintenance, and operational robustness. By designing and developing a prototype implementation of the circuitry required for management and harvesting of energy, we demonstrate a SOLARCAP system that ensures safe device operation within the permitted voltage range.

The amount of data processed annually over the Internet has crossed the zetabyte boundary, yet th... more The amount of data processed annually over the Internet has crossed the zetabyte boundary, yet this Big Data cannot be efficiently processed or stored using today's mobile devices. Parallel to this explosive growth in data, a substantial increase in mobile compute-capability and the advances in cloud computing have brought the state-ofthe-art in mobile-cloud computing to an inflection point, where the right architecture may allow mobile devices to run applications utilizing Big Data and intensive computing. In this paper, we propose the MObile Cloud-based Hybrid Architecture (MOCHA), which formulates a solution to permit mobile-cloud computing applications such as object recognition in the battlefield by introducing a mid-stage compute-and storage-layer, called the cloudlet. MOCHA is built on the key observation that many mobile-cloud applications have the following characteristics: 1) they are compute-intensive, requiring the compute-power of a supercomputer, and 2) they use Big Data, requiring a communications link to cloud-based database sources in near-real-time. In this paper, we describe the operation of MOCHA in battlefield applications, by formulating the aforementioned mobile and cloudlet to be housed within a soldier's vest and inside a military vehicle, respectively, and enabling access to the cloud through high latency satellite links. We provide simulations using the traditional mobile-cloud approach as well as utilizing MOCHA with a mid-stage cloudlet to quantify the utility of this architecture. We show that the MOCHA platform for mobile-cloud computing promises a future for critical battlefield applications that access Big Data, which is currently not possible using existing technology.

This paper presents an overview of passive radio frequency (RF) energy reception and power harves... more This paper presents an overview of passive radio frequency (RF) energy reception and power harvesting circuits for isolated communications and computing systems lacking access to primary power sources. a unified understanding of the energy harvesting alternatives is provided, followed by an elaborate study of RF energy harvesting within the context of embedded systems. a detailed discussion of RF technologies ranging from the directed communications signal reception to dispersed ambient power harvesting is provided. A comparative focus on design tradeoffs and process alterations is provided to represent the diversity in the applications requiring wireless RF harvesting units. Also included is an analysis of system combinations, and how wake up units, active storage, and duty cycling play roles in the consumption and harvesting of RF energy.

As servers are placed in diverse locations in networked services today, it becomes vital to direc... more As servers are placed in diverse locations in networked services today, it becomes vital to direct a client's request to the best server(s) to achieve both high performance and reliability. In this distributed setting, non-negligible latency and server availability become two major concerns, especially for highly-interactive applications. Profiling latencies and sending redundant data have been investigated as solutions to these issues. The notion of a cloudlet in mobile-cloud computing is also relevant in this context, as the cloudlet can supply these solution approaches on behalf of the mobile. In this paper, we investigate the effects of profiling and redundancy on latency when a client has a choice of multiple servers to connect to, using measurements from real experiments and simulations. We devise and test different server selection and data partitioning strategies in terms of profiling and redundancy.

2012 IEEE Symposium on Computers and Communications (ISCC), 2012

Face recognition applications for airport security and surveillance can benefit from the collabor... more Face recognition applications for airport security and surveillance can benefit from the collaborative coupling of mobile and cloud computing as they become widely available today. This paper discusses our work with the design and implementation of face recognition applications using our mobile-cloudlet-cloud architecture named MOCHA and its initial performance results. The challenge lies with how to perform task partitioning from mobile devices to cloud and distribute compute load among cloud servers (cloudlet) to minimize the response time given diverse communication latencies and server compute powers. Our preliminary simulation results show that optimal task partitioning algorithms significantly affect response time with heterogeneous latencies and compute powers. Motivated by these results, we design, implement, and validate the basic functionalities of MOCHA as a proof-of-concept, and develop algorithms that minimize the overall response time for face recognition. Our experimental results demonstrate that highpowered cloudlets are technically feasible and indeed help reduce overall processing time when face recognition applications run on mobile devices using the cloud as the backend servers.

Enabling Real-Time Mobile Cloud Computing through Emerging Technologies, 2015

Different forms of parallel computing have been proposed to address the high computational requir... more Different forms of parallel computing have been proposed to address the high computational requirements of many applications, following the principle that large computational problems can often be divided into smaller ones. Building on advances in parallel and distributed computing, volunteer computing has been shown to be an efficient way to exploit the computational resources of devices that are available around the world and that are under utilized for most of their time. The idea of including mobile devices, such as smartphones and tablets, in existing distributed volunteer computing systems has recently been investigated.

Ad Hoc Networks, 2008

IEEE Transactions on Mobile Computing, 2008

2012 IEEE Symposium on Computers and Communications (ISCC), 2012

Enabling Real-Time Mobile Cloud Computing through Emerging Technologies, 2015